Old cites are not regenerative,so the protection of old cites is very important,which is the guarantee of sustainable development of the old cites' tourism.Under the conditions that the protection of old cites lack of funds,it is a realistic choice for protecting the cultural heritages that tourism funds the protection.This paper taking Pingyao old city as a case,analyzes the positive and negative relationship between the protection of old cites and the development of tourism,seeks for how the protection of old cites and the development of tourism can form a benign cycle and finally puts forward corresponding measures.